With development of the electronic technical, a computing system is widely used. For example, from handheld electronic equipments (e.g., tablet personal computer, e-book, digital camera, and so on), to large electronic equipments (e.g., server, computing base station, and so on), all require the computing system. A computing platform comprises a central processing unit (CPU) and other components. The CPU is utilized to interpret machine readable instructions and process all data in the computing system. A voltage regulator is needed to power the CPU. And a battery is utilized to provide power to the voltage regulator when the computing platform disconnects from an external power source. Thus, a battery charging circuit is also needed to provide a system voltage to the voltage regulator and charge the battery when the computing platform connects to the external power source.
As user requirements increasing, the CPU needs to boost performance at times, e.g., increasing an operating frequency. However, instantaneous power needed by the CPU may increase dramatically to support the boosted performance. Thus, the battery charging circuit should be designed to satisfy demands of instantaneous power consumption.